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Home , Europa (moon), Moon

The High Priority and Relevance of

Galileo Galilei's discovery of of to that of exploration6. In 2003, the in 1610 advanced the Copernican decadal Exploration Survey7 of Revolution. Now nearly 400 years later, one the NRC called for a Europa orbiting space- of these moons–Europa–has the potential for craft as the single highest priority large "flag- discoveries just as profound. Europa's icy sur- ship class" exploration mission for the decade face is believed to hide a global subsurface 2003-2013. Such a mission would with nearly three times that of confirm the existence of Europa's subsurface 's oceans1. The 's surface is , ocean, characterize in detail the moon's sur- with a nominal age of 50 million years, imply- face and icy shell, and conduct reconnaissance ing that it is most likely geologically active vital for future landed exploration. 2 today . The primitive materials that nourish Much of NASA's current planetary explo- have rained onto Europa throughout solar ration , and that planned for the future in system history, are created by radiation chem- NASA's exploration vision8, is placed on the istry at its surface, and may pour from vents at 3 astrobiological potential of Mars, which likely the ocean's deep bottom . On Earth, microbial once had liquid on its surface and may take advantage of environ- have water underground today. Given that Eu- mental niches arguably as harsh as within Eu- 4 ropa appears to currently possess the three ropa's subsurface ocean . If the subsurface main criteria for the existence of life as we of this Galilean moon were found to know it (liquid water, sufficient energy contain life, the discovery would spawn an- sources, and organic building blocks)3, Europa other revolution, this time in our understand- is equally as promising a place to look for ex- ing of life in the . tant life in our solar system. Moreover, the The astrobiological potential of Europa proximity of Mars to Earth means that the two has been revealed in recent years through could have exchanged biological mate- spectacular data from the spacecraft. rials over solar system history, transferred in The existence of liquid water in the outer solar like those found on Earth9. Thus, system was once thought a remote possibility, life originating on one could have but the combination of geological, gravita- spread to its neighbor, plausibly resulting in a tional, and observations and single tree of life with a common ancestor at theory make it appear quite possible–even some point early in biological history. On the likely–that liquid water exists beneath Eu- other hand, transfer of biological materials ropa's icy surface1. It is now recognized that between Earth and distant Europa is quite un- may exist within many large icy satel- likely, so any life on Europa would probably lites, but Europa's inferred thin shell and have a completely independent origin. If or- potentially active surface-ocean exchange ele- ganisms exist there, Europa would provide vate its priority for astrobiological explora- essential evidence for a distinct origin, and tion. A Europa mission is the first step in un- perhaps a distinct chemistry, of life. derstanding the potential for icy as To fully understand the planetary context abodes for life. and origin(s) of life in the solar system, a sys- The high priority and relevance of Europa tematic program of astrobiological exploration to scientific advancement has been recognized is necessary for both Mars and Europa. Eu- by several national committees. In 1994, the ropa is a challenging exploration target be- Space Studies Board of the National Research cause of significant travel times, a severe ra- Council recognized that Europa's and diation environment, and the lack of a sub- along with its potential for extra- stantial for aerobraking. Moreo- terrestrial life assigned Jupiter system explora- ver, is a vital issue be- tion a priority equal to that of the exploration cause any forward contamination of Europa's of Mars5. In 1999, the Committee on Plane- ocean at one location could enable global ac- tary and Lunar Exploration of the National cess for contaminants10. Nonetheless, Europa's Research Council (NRC), while acknowledg- priority as an exploration target requires that ing the technological challenges involved in technology hurdles be addressed with suffi- Europa exploration, reaffirmed that Europa cient near-term investment. Technology shar- exploration should be assigned a priority equal ing and complementarity between Europa and Mars exploration should be encouraged, most Alfred McEwen, notably in life detection experiments and Xuan-Min Shao, Los Alamos Erik Asphaug, University of California Santa Cruz planetary protection. Bill Kurth, University of Iowa The extremely high priority of Europa ex- Rosaly Lopes, Jet Propulsion Laboratory ploration calls for concomitant attention and Wanda Davis, dedication to Europa exploration not only in Jody W. Deming, University of Washington the distant future but in the present decade, Dave Atkinson, University of Idaho and with priority equal to that of Mars. Europa Andrew Potter, National Optical Obs. Wing Ip, National Central University of Taiwan exploration, which has the potential for find- Bernd Giese, DLR Institute of Planetary Research ing extant life in our solar system, must be Amy C. Barr, University of Colorado central not only to NASA's exploration vision, Irene M. Engle, U.S. Naval Academy but to its exploration implementation. Geoffrey C. , Wheaton College

Bruce Hapke, University of Pittsburgh Signed: Heidi B. Hammel, Space Institute Robert T. Pappalardo, University of Colorado Nilton O. Renno, Cynthia , SETI Institute Frank Carsey, Jet Propulsion Laboratory Louise M. Prockter, Applied Physics Laboratory Herb Breneman, Jet Propulsion Laboratory Francis Nimmo, Univ. California Los Angeles Louis Irwin, University of Texas El Paso Paul M. Schenk, Lunar and Planetary Institute Christopher Russell, Univ. California Los Angeles Baerbel Lucchitta, U.S. Geological Survey Dave Slater, Southwest Research Institute , Hajo Eicken, University of Alaska Fairbanks Keith Raney, Applied Physics Laboratory Eric Grosfils, Pomona College Kandy S. , Lockheed Martin Space Operations Richard Reinert, Aerospace John Spencer, Southwest Research Institute Tom McCord, Institute Jeffrey M. Moore, Ames Research Center P. Winebrenner, University of Washington David Kohlstedt, University of Minnesota Susanne Neuer, Arizona State University Robert W. Carlson, Jet Propulsion Laboratory Chris Paranicas, Applied Physics Laboratory Kevin P. Hand, Stanford University / SETI Institute , University of Arizona Steve Ostro, Jet Propulsion Laboratory David A. , Arizona State University Hoppa, Raytheon Tom Hill, Rice University Imke de Pater, University of California Berkeley Beth E. Joseph, Ithaca College Blaney, Jet Propulsion Laboratory Carol Stanley, Jet Propulsion Laboratory David Warmflash, University of Houston David Morrison, Ames Research Center Hunter Waite, University of Michigan William Durham, Lawrence Livermore Donald Blankenship, University of Texas Austin Masatoshi Yamauchi, Swedish Inst. Space Physics Chris McKay, Ames Research Center Patricio Figueredo, Exxon-Mobil Nalin Samarasinha, National Optical Astronomy Obs. Robert Kovach, Stanford University Reggie L. Hudson, Eckerd College / Roger C. Wiens, Lawrence Livermore Norbert I. Köemle, Austrian Academy of Sciences Leslie Tamppari, Jet Propulsion Laboratory Joe Burns, Cornell University Simon Kattenhorn, University of Idaho Mitchell Sogin, Marine Biological Laboratory Wayne F. Zimmerman, Jet Propulsion Laboratory Paul Feldman, Johns Hopkins University Robert E. Johnson, University of Virginia Will Grundy, Observatory Sean Solomon, Carnegie Institution Tracy K.P. Gregg, University at Buffalo William Smyth, Atmospheric & Environ. Research Dirk Schulze-Makuch, Washington State University Candice Hansen, Jet Propulsion Laboratory Chris Chyba, Stanford University / SETI Institute

Michael J.S. Belton, Belton Space Expl Initiatives, LLC 1 Greeley, R., C. Chyba, J. W. , T. McCord, W. B. McKinnon, R. T. Pappalardo, and P. Figueredo, Geology of Europa, in Jupiter: The Planet, Satellites & (F. Bagenal et al., eds.), pp. 329-362, 2004. 2 Zahnle, K., P. Schenk, H. Levison, and L. Dones, Cratering rates in the outer Solar System, , 163, 263–289, 2003. 3 Chyba, C. F. and C. B. Phillips, Possible and the search for life on Europa, Proc. Nat. Acad. Sci., 98, 801-804, 2001. 4 Horikoshi, K. and W.D. Grant (eds.), Extremophiles: Microbial Life in Extreme Environments, -Liss: New York, 1998. 5 Space Studies Board, National Research Council, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press, Washington, D.C., 1994. 6 Committee on Planetary and Lunar Exploration, National Research Council, A Science Strategy for the Exploration of Europa, National Academy Press, Washington, D.C., 1999. 7 Solar System Exploration Survey, Space Studies Board, National Research Council, New Frontiers in the Solar System: An Integrated Exploration Strategy, National Academy Press, Washington, D.C., 2003. 8 President's Commission on Implementation of United Spates Policy, A Journey to Inspire, Innovate, and Discover, Washington D.C., 2004.

9 Mileikowsky, C., F. Cucinotta, J.W. Wilson, G. Horneck, L. Lindgrin, H.J. Melosh, H. Rickman, and M. Valtonen, Natural transfer of viable microbes in space: 1. From Mars to Earth and Earth to Mars, Icarus, 145, 391-427, 2000. 10 Space Studies Board, National Research Council, Preventing the Forward Contamination of Europa, National Academy Press, Washington, D.C., 2000.